fix(builder): Quote empty default values

Author: yash27-lab

clap_builder/src/util/escape.rs

@@ -5,7 +5,7 @@ pub(crate) struct Escape<'s>(pub(crate) &'s str);
 
 impl<'s> Escape<'s> {
     pub(crate) fn needs_escaping(&self) -> bool {
-        self.0.contains(char::is_whitespace)
+        self.0.is_empty() || self.0.contains(char::is_whitespace)
     }
 
     #[cfg(feature = "help")]

tests/builder/help.rs

@@ -2044,7 +2044,7 @@ fn empty_default_value() {
 Usage: default [OPTIONS]
 
 Options:
-      --arg <argument>  Pass an argument to the program. [default: ]
+      --arg <argument>  Pass an argument to the program. [default: ""]
   -h, --help            Print help
   -V, --version         Print version